<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>float + overflow: hidden</title>
</head>
<style>
    .parent {
        overflow: hidden;
        zoom: 1;
    }
    .left {
        float: left;
        margin-right: 20px;
    }
    .right {
        overflow: hidden;
        zoom: 1;
    }
</style>
<body>
    <div class="parent" style="background-color: lightgrey;">
        <div class="left" style="background-color: lightblue;">
            <p>left</p>
        </div>
        <div class="right"  style="background-color: lightgreen;">
            <p>right</p>
            <p>right</p>
        </div>        
    </div>
</body>
</html>